Corrosion resistant edge tools such as razor blades

ABSTRACT

STEELS SUITABLE FOR MAKING CORROSION-RESISTANT EDGED TOOLS (E.G., RAZOR BLADES) CONTAIN CHROMIUM AND CARBON, AND MAY CONTAIN SILICON, MANGANESE, MOLYBDENUM STEN, COPPER, COBALT, NICKEL, NIOBIUM, TANTALUM, TITANIUM VANADIUM, ZIRCONIUM, BORON, OR BERYLLIUM. THE RATIO OF CHRONUM TO CARBON IS LESS THAN 30:1: THE CARBON CONTENT IS 0.3-0.5 WT. PERCENT; AND THE CHRONIUM CONTENT IS 9.010.8 WT. PERCENT. A TOOL FORMED FROM A STEEL OF THIS CLASS HAS A HARDNESS EXCEEDING VPN 800 IN THE HARDENED CONDITION, AND A HARDNESS AFTER TEMPERING UP TO 400*C. WITHIN THE RANGE VPN 650-800.

July 30 1974 3,826,697

JAN-CHESTER H. 0. CARI-EN ET L CORROSION RESISTANT EDGE TOOLS SUCH AS RAZOR BLADES Original Filed June 1., 1970 INVENTORS I ATTORNEYS United States Patent 01 ice 3,826,697 Patented July 30, 1974 3,826,697 CORROSION RESISTANT EDGE TOOLS SUCH AS RAZOR BLADES Jan-Christen Henric Ovesson Carlen and Claes Rertil Bergqvist, Sandviken, Sweden, assignors to Sandvrkens Jernverks Aktiebolag, Sandviken, Sweden Continuation of abandoned application Ser. No. 42,050, June 1, 1970. This application Oct. 17, 1972, Ser. No.

Int. Cl. C22c 39/14 US. Cl. 148-37 3 Claims ABSTRACT OF THE DISCLOSURE This is a continuation of application Ser. No. 42,050, filed June 1, 1970, now abandoned.

The present invention relates to improvements in corrosion-resistant edge tools, and more specifically to hardened steel edge tools such as razor blades having a very good corrosion resistance, a high cutting edge hardness and a structure free from deleterious carbide grains. The invention also comprises a method for the manufacture of the tools. The hardness of these tools normally exceeds VPN 800 (Vickers hardness, 0.5 kg. load) in the hardened condition and after tempering up to 400 C. the hardness may be VPN 650-800 depending on the tempering temperature.

Previously, corrosion-resistant edge tools such as razor blades have been made from high chromium steels having high or medium high content of carbon and being hardened from a temperature exceeding 1000 C. As examples can be mentioned steel containing 13-14% chromium, 0.9-1.1% carbon (type A) and 13-14% chromium and 05-07% carbon (type B), the remainder being substantially all iron, possibly with minor additions of one or more further elements such as manganese, copper, molybdenum and cobalt.

The tools made of these steels have in several essential respects been found not entirely satisfactory. Thus, steels of the type A when hardened to a hardness close to VPN 800 acquire a structure including a large number of coarse carbide grains within the range of 3-30 micron (maximum linear dimension) which render it impossible to obtain a smooth cutting edge on a tool of this steel, as these grains are easily torn out during the grinding of the cutting edge and give a frayed contour and surface. Moreover, the corrosion resistance of these steels is only moderate. Steels of the type B have less coarse carbide grains and a somewhat better corrosion resistance than have the steels of the aforementioned type, but the maximum hardness obtained by hardening is less than that for type A, which adversely influences the duration of edge sharpness of tools manufactured from the same.

The purpose of the present invention is to provide corrosion-resistant edge tool such as a razor blade having an iinproved corrosion resistance in combination with superior edge sharpness and smoothness and improved temper resistance.

The appended drawing is a diagram showing the preferred contents of carbon and the sum of chromium, onehalf of the molybdenum and one-quarter of the tungsten according to the present invention. Said sum is designated Y in the diagram.

According to the invention the edge tools, e.g. razor blades, are made from a hardenable steel having a very good corrosion resistance and a hardness exceeding VPN 800 in the hardened condition and a hardness after tempering up to 400 C. within the range VPN 650-800 depending on the tempering temperature. The steelwhich has a good workability, such as excellent cold rolling properties-is characterized in that it in addition to carbon and chromium, whereby the chromium-carbon ratio shall be less than 30/1, contains 0-0.8% silicon; 0-1.0% manganese; 0-1.5% molybdenum; and 0-1% each of a member of the group consisting of nickel, cobalt, copper, niobium, tantalum, titanium, vanadium, zirconium, boron, and beryllium, the total of all the last said members being a maximum of 1%; and the remainder being substantially all iron. The corrosion-resistant razor blades of the present invention are composed of a steel having a martensitic structure. They exhibit improved edge smoothness, and a hardness, after tempering, within the range VPN 650- 800. Said steel has the following composition, in percentages by weight: carbon, 0.30-0.50%; chromium, 9.0- 10.5%; manganese, 0.2-0.7%; silicon, 0.2-0.7%; molybdenum, 0-1.25%; the remainder being iron with unavoidable impurities. Furthermore, the amounts of carbon and the sum of the amounts of chromium and one-half of the molybdenum should be chosen in accordance with the area ABCDEFA in the accompanying diagram, wherein the said sum is designated Y. Thus, when a low carbon content is chosen we have found that the chromium content-and, when molybdenum is present, the sum of the chromium content and one-half of the molybdenum content and onequarter of the tungsten contentshould in general also be low. The limiting conditions defined by the coordinates of the area ABCDEFA are the following: A 9.0/0.3; B 10.0/0.3; C 12.0/0.4; D 12.0/05; E /05; and F 9.0/0.4.

The carbon content has to lie within the range 0.30- 0.50% as seen from the diagram. Normally, the carbon content should be at the most 0.45% e.g. chosen within the narrower range 0.35 %0.45%. Further, the chromium content as a rule be held within the range 0.5-10.8%, preferably 9.5-10.5%. It has been found that excellent results are obtained if the chromium-carbon ratio lies within the range It is also preferred that the sum of the contents of chr0- mium and one-half of the molybdenum, Should be within the range 9.5-11.25%. The content of molybdenum should normally be at most 1.25%, e.g., between 0.2 and 1.25%. The silicon content should preferably be 0.2-0.7% and the manganese content likewise 0.2-0.7%. The amount of any element of the group consisting of nickel, cobalt, copper, niobium, tantalum, titanium, vanadium, zirconium, boron and beryllium present in the composition should normally not exceed 0.5% and the total of all these elements should also not exceed 0.5%.

A preferred range of components of the steel composition from which the razor blades of the present invention are to be formed is as follows:

Wt. percent Carbon 0.35-0.45 Chromium 9.5-10.5 Manganese 0.2-0.7 Silicon 0.2-0.7 Molybdenum 0.2-1.2

Remainder iron with unavoidable impurities not exceeding 0.5 wt. percent.

The preferred specific steel composition is (stated in percentages by weight) as follows:

Iron, balance save for unavoidable impurities.

This composition is so fully balanced that its content of carbide grains coarser than 5 microns per mm. is nil. Maximum hardness in VPN after the treatment described The steels previously used for edge tools such as razor blades have had a non-balanced composition which means that their contents of carbon and chromium have been in excess of what would be useful when the steel was heat treated. Thus the surplus of carbon and chromium has been found as carbide grains in the hardened steel while the matrix has had substantially less carbon and chromium contents than could be learned by the chemical analysis of the steel.

According to the present invention the composition should be balanced in such a way that the analysis of the steel and that of the matrix are substantially the same. One of the advantages gained by the steel according to the invention is that the composition of the matrix after hardening will be practically constant irrespective of changes in the hardening conditions. This means also that the corrosion resistance will be unchanged and that the steel will be insensible to changes in the heat treatment conditions. A further advantage in comparison with the previous corrosion-resistant steels used is the lower content of chromium which is of importance also with respect to costs.

The hardness of a hardened steel depends, i.a., on the carbon content of the steel. However, if the M -temperature of the steel-the temperature when the transforma tion of austenite into martensite beginsis lowered by the addition of convenient amounts of alloying elements to such an extent that practically no self-tempering of the martensite will occur after the hardening of the steel, a hardness exceeding VPN 800 may be reached when the carbon content is as low as about 0.3%. If on the other hand the M -temperaturethrough adding too large amounts of alloying elements to the steel-is unduly lowered, the austenite transforms only partly into martensite with the result that the hardness will not be sufficiently high even if a martensite-promoting, low-temperature cooling is resorted to. The prior steels used for the manufacture of corrosion-resistant edge tools such as razor blades have not had compositions conveniently balanced, with the result that the maximum hardness reached by these steels has been considerably less than wanted. Nor has it been possible by these steels to obtain such a uniform composition in the matrix as in the matrix of the steel according to the invention. Thus the presence of large amounts of carbide grains in said prior steels gave rise to variations in the chemical composition round the grains, which in turn reduced the maximum hardness obtainable by hardening.

The superior properties of the steel according to the invention in comparison with previously used corrosionresistant steels for edge tools will be further explained in the following by way of examples.

The structure of the steel as cold-rolled is of considerable importance for producing an excellent edge. Thus the presence of coarse carbide grains is a serious disadvantage, as they (as was earlier mentioned) are easily torn out during the grinding of the cutting edge and leave the edge with a frayed contour and surface. In the example below, the steels A and B represent previously used razor blade steels while the steel C2 represents a steel according to the invention.

Carbide grains per Percent mm. coarser than5 C Si Mn Cr Mo micron The hardness of corrosion-resistant chromium steels is dependent on the temperature used for the hardening, the cooling from the hardening temperature and the tempering temperature. For steels which, contrary to the steel according to the invention, do not have a balanced composition there is always by a given hardening time and a fixed cooling method one hardening temperature, which gives maximum hardness. By subsequent tempering at -150 C. it is impossible somewhat to increase said hardness. In the following examples in which steels A and B represent prior razor blade steels and C2 and C3 steels according to the invention the maximum hardness has been obtained by using a hardening time of 40 seconds, a cooling from the hardening temperature to room temperature and thereafter to 70 C. and a subsequent tempering at 100 C. in boiling water, thereby developing, as known, a martensite structure.

Percent; Maximum hardness C Si Mn Cr Mo W VPN The high hardness of the steels according to the invention facilitates edge grinding, improves the quality, and contributes also to a prolongation of the useful life of the edges especially ifas is common-the edges are coated at a relatively low temperature, e.g., up to 200 C. and preferably up to 150 C., with a material (e.g., a fluorocarbon) for enhancing the cutting characteristics.

In spite of its relatively low content of chromium and other corrosion-preventing elements such as molybdenum and tungsten, the steel according to the invention has an excellent corrosion resistance. A comparison of the corrosion rate in 0.5% acetic acid for the aforementioned prior steels A and B and the steels C2 and C3 of the present invention is given in the table below. All the steels are hardened and tempered to maximum hardness.

Corrosion rate, mm./ year A 98 B 5.0 C2 4 0 C3 4 6 It is evident from this table that the steels C2 and C3 are considerably more corrosion-resistant than is steel A and approximately equivalent to steel B in spite of a lower content of alloying elements.

The invention also relates to a method for the manufacturing of edge tools such as razor blades from steels according to the invention. According to the method aspect of the invention, the steel is cold rolled in strip form to the desired thin dimension, e.g. 0.05-0.5 mm., after which a shaping e.g. punching may be done. The cold rolled steep strip is then hardened to high hardness by heating to a temperature within the range 1050-1125 C., preferably about 1100 C. with subsequent cooling to room temperature or lower, e.g. between the range 20 C. and C. After the hardening and a possible subsequent tempering within the range 75-125 C., e.g.

about 100 C. to a hardness level exceeding VPN 800, the cutting edges are shaped by grinding or the like. Finally the material may be tempered during a limited period of time-for instance, for about a minute up to one or a few hours-at a temperature up to 400 C., e.g. about 150 C. The hardness of the steel after the said final tempering is at least VPN 650 and-depending on the temper temperature-lies within the range VPN 650-800.

All the percentages mentioned throughout this specification and in the appended claims are percentages by weight.

The invention is of course not limited to the described embodiments but comprises any product within the scope of the appended claims.

We claim:

1. A corrosion-resistant razor blade composed of steel with a martensitic structure, said blade having improved edge smoothness and a hardness after tempering within the range VPN 650-800, said razor blade being made from a steel consisting essentially of in percent by weight carbon, 0.350.45%; chromium 9.5-l0.5%; manganese, 0.2-0.7%; silicon, 0.20.7%; molybdenum, 0.2-1.2; the remainder being iron with unavoidable impurities, the ratio of chromium content to carbon content being within the range 20:1 to 28:1, and falls within the area ABCDEFA of the diagram of the accompanying drawing.

2. A corrosion-resistant razor blade as defined in claim 1, wherein the steel has the following composition (in weight percentages):

Carbon 0.40 Chromium 10.1 Manganese 0.38 Silicon 0.42 Molybdenum 0.90

Remainder iron with unavoidable impurities.

3. A corrosion-resistant razor blade as defined in claim 1, wherein the steel has the following composition (in weight percentages);

Carbon 0.42 Chromium 10.0 Manganese 0.38

Silicon 0.34 Molybdenum 0.87 Remainder iron with unavoidable impurities.

References Cited UNITED STATES PATENTS 3,595,643 7/1971 Boyce -126 C 2,123,144 7/1938 Newell 75-126- C 2,590,835 4/1952 Kirkby 75-126 C 2,801,916 8/1957 Harris 75-126- C 2,934,430 4/1960 Klaybor 75-126 C 3,640,114 2/1972 Foley 75-126 C HYLAND BIZOT, Primary Examiner US. Cl. X.R.. 75-126 mrm srAs mrrwr @rrrrr crrrrrmrr @r mrrrrrrrr Patent No. 2.826.697 Dated July 3om WW Invenr fl .mnmcmmmr HA 0.. rim-mm m; 21

It is certified that error appears in the above-identified patent and that said Letters Patanr are hereby wrrecred as shown below? 5 [73] Assiggmww iizirarmiviirrrrr Swedrm Signed arm aealed this 22nd day of October 197 (SEAL) Attesrs McCoy Mu GIBSON Attesring Officm' Ga MARSHALL DANN Coissioner of Parents USCIOMM-DC 60376-P69 fi us. GOVERNMENT PRINTING oWlcE I960 0-auu-J5A,

FORM PC4050 (IO-'69) 

